The present invention relates to gate valves and other devices wherein one flat plate slides against another flat plate, and more particularly to an improved method for applying a hard wear-resistant surface to a softer metal body member, such as a gate valve gate and a gate valve seat insert.
In the past, hard wear-resistant surfaces have been formed on parts of gate valves and the like by depositing an alloy in powder form on the surface, then heating it to a molten state. After cooling, a grinding procedure follows to reduce the hard coat to tolerance, such that the part can be used in a gate valve or slide, wherein the valve gate has a sealed liquid-tight relationship with the valve seat against which it slides. This method results in a waste of considerable material which is ground off the entire coated surface, and further the stresses and contamination caused by heat build-up tend to cause cracks, porosity and warpage. The process has proven, therefore, somewhat uneconomical, and is not the trouble-free process which is desired.
It has been suggested in U.S. Pat. No. 3,418,708 that a valve disc, and an annular valve seat for a globe valve located inside a recess, can be bonded in position by a beam of high energy charged particles directed parallel to the weld joint surfaces. U.S. Pat. No. 4,306,139 discloses a method for arc welding a hard material consisting of nickle and tungsten carbide particles, directly to an iron base member. No known prior art, however, discloses a method of fixing a relatively large area thin facing sheet to a gate valve or other flat plate to provide a wear-resistant surface thereon in a trouble-free, economical manner, where the facing and gate or seat insert body member are bonded in a fluid-tight, distortion-free relationship.
One of the prime objects of the present invention is therefore to provide a method of economically and reliably making gates and seat inserts for gate valves, having a hardened surface on one or both sides, which will be wear-resistant and resist corrosive influences.
Another object of the invention is to provide a method of electron beam welding such parts in a manner which avoids warpage, and avoids the formation of cracks and porosity.
Still another object of the invention is to provide parts for gate valves having hard, abrasive-resistant facings which effectively resist the galling that such gate valve parts otherwise experience in use, and which are capable of withstanding the high pressures to which they are subjected when in use, without destructing.